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United States Patent |
5,229,977
|
Owen
|
July 20, 1993
|
Directional underwater acoustic pulse source
Abstract
A closed-cycle combustion low-frequency acoustic pulse source for use
underwater. An elongated combustion chamber, having a first end and a
second end and an elongated elastic sleeve, is filled with a
stoichiometric mixture of oxygen and hydrogen from an electrolyzer. When
the mixture is ignited at the first end of the chamber, a longitudinally
traveling flame front is initiated at the first end of the chamber. The
moving front results in a traveling thermal pressure pulse. The pressure
pulse is communicated to the surrounding underwater medium producing a
generally uni-directional acoustic pressure pulse along the longitudinal
axis of the elongated chamber. An alternative embodiment utilizes an array
of sources disposed along the generally horizontal longitudinal axis of
the array.
Inventors:
|
Owen; Thomas E. (Helotes, TX)
|
Assignee:
|
Southwest Research Institute (San Antonio, TX)
|
Appl. No.:
|
900171 |
Filed:
|
June 17, 1992 |
Current U.S. Class: |
367/145; 181/117; 181/118 |
Intern'l Class: |
G01V 001/06; G01V 001/38 |
Field of Search: |
367/145
181/116,117,118
|
References Cited
U.S. Patent Documents
1500243 | Jul., 1924 | Hammond | 181/118.
|
2679205 | May., 1954 | Piety | 181/118.
|
3099813 | Jul., 1963 | Anderson | 181/118.
|
3380551 | Apr., 1968 | Lang | 181/118.
|
3563334 | Feb., 1971 | McCarter | 181/118.
|
3587775 | Jun., 1971 | Becker | 181/118.
|
3620327 | Nov., 1971 | Savit | 181/118.
|
3658149 | Apr., 1972 | Neal et al. | 181/118.
|
3669213 | Jun., 1972 | Mollere | 181/118.
|
3700066 | Oct., 1972 | Knight et al. | 181/118.
|
3895688 | Jul., 1975 | Bouyoucos | 181/117.
|
4300653 | Nov., 1981 | Cao et al. | 367/144.
|
4599712 | Jun., 1986 | Chelminski | 367/144.
|
5013418 | May., 1991 | Wullenweber et al. | 204/253.
|
Foreign Patent Documents |
554517 | Apr., 1977 | SU.
| |
681399 | Aug., 1979 | SU.
| |
Primary Examiner: Eldred; J. Woodrow
Attorney, Agent or Firm: Gunn, Lee & Miller
Claims
I claim:
1. A closed-cycle combustion acoustic pulse source for use underwater
comprising:
An elongated combustion chamber having a first end and a second end and an
elastic outer sleeve extending the length of said chamber;
a means for igniting, at said first end of said combustion chamber, a
stoichiometric mixture of oxygen and hydrogen contained in said chamber to
initiate a flame front which travels from said first end of said chamber
to said second end of said chamber creating a traveling thermal pressure
pulse, said thermal pressure pulse in turn generating a generally
uni-directional acoustic pressure pulse in said underwater along the
longitudinal axis of said elongated chamber, said chamber further
comprises an elongated core member cooperating with said elastic sleeve to
provide an annular combustion zone to receive a sufficient volume of said
mixture of oxygen and hydrogen to produce a preferred frequency of said
acoustic pressure pulse when said volume is ignited;
an elongated electrolyzer containing an aqueous electrolyte for producing
said mixture of oxygen and hydrogen upon activation of an electrolysis
power source;
a means for delivering said mixture of oxygen and hydrogen to said
combustion chamber prior to ignition of said mixture and for delivering
condensate to said electrolyzer after ignition of said mixture.
2. The source of claim 1 wherein said preferred frequency is in the 30-300
Hz range.
3. The source of claim 1 wherein said electrolyzer further comprises a
plurality of electrolysis cells along a central length of said
electrolyzer.
4. The source of claim 1 wherein said combustion chamber and said
electrolyzer are positioned in said underwater with said longitudinal axis
of said chamber in a generally horizontal orientation, said electrolyzer
positioned beneath said chamber.
5. The source of claim 1 wherein said means for delivering said mixture of
oxygen and hydrogen to said combustion chamber prior to ignition of said
mixture and for delivering condensate to said electrolyzer after ignition
of said mixture comprising a strut connected to and extending along the
length of said chamber and said electrolyzer, said strut having a
multiplicity of gas, and condensate passageways communicating said
electrolyzer to said chamber.
6. A method for generating a generally uni-directional acoustic pressure
pulse in an underwater environment comprising:
producing in an electrolyzer a stoichiometric mixture of oxygen and
hydrogen;
delivering said mixture to an elongated combustion chamber having a first
end and a second end and an elastic outer sleeve extending the length of
said chamber;
igniting said mixture at said first end of said chamber to initiate a flame
front which travels from said first end of said chamber to said second end
of said chamber creating a traveling thermal pressure pulse, said thermal
pressure pulse in turn generating said generally uni-directional acoustic
pressure pulse in said underwater environment wherein the frequency of
said acoustic pressure pulse is determined by varying the volume of said
delivered mixture in said chamber by varying the volume of a core element
positioned within said chamber, said acoustic pulse traveling in the
direction of said length of said chamber;
collecting condensated steam after said igniting for delivery to said
electrolyzer.
7. The method of claim 6 wherein said frequency is in the range of 30-300
Hz.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for and the use of a
closed-cycle chemical combustion process as the means for producing
accurately controlled and repeatable high-power, low-frequency, underwater
sound pulses.
In general, the most effective low-frequency ocean acoustic source
techniques have been non-reciprocal methods deriving their excitation
energy from chemical forms (solid explosives; gas combustion), pneumatic
forms (air gun), hydraulic forms (water gun; hydrodynamic), mechanical
vibrators (electrical; hydraulic drive), motor-driven hammer/acoustic
diaphragms, electrical discharge forms (sparkers, boomers), and cavity
implosion devices. The most thoroughly exploited of these technologies are
pneumatic and hydraulic sources (for off-shore seismic exploration) and
the electrical discharge forms (for off-shore sub-bottom profiling and
shallow marine exploration). The electric arc discharge technique had
recently been refined to provide higher energy density together with the
important ability to generate efficient controlled-spectrum pulses in the
frequency range of about 200-2,000 Hz at input energy levels of about
1,200 Joules per pulse. With appropriate further development, this
technique offers the prospect for becoming a low-maintenance ocean
acoustic pulse source capable of generating accurately timed acoustic
pulse signals at lower frequencies and having an input energy level up to
about 10,000 Joules per pulse. However, with a practical
electrical-to-acoustical energy conversion efficiency of about 15 percent,
other acoustic pulse source techniques having higher energy conversion
efficiency become important alternatives, provided that they can meet the
practical requirements of accurate pulse timing and accurate repetitive
pulse wavelet generation.
Chemical energy sources offer the highest available energy density and, in
general, because of their direct energy release in the water medium, are
the most efficient in converting their chemical reaction potential energy
to radiated acoustic energy. For example, large underwater explosions are
estimated to transform more than 50 percent of their latent energy into
the outgoing shock wave pulse; a conversion process aided by the nonlinear
response effects of such a finite amplitude source mechanism.
Nevertheless, such sources approach the ideal performance effectiveness
since the radiation efficiency of a simple linear acoustic impulsive
source is inherently limited to 50 percent. That is, half of the total
source energy is stored in the incompressible near field (i.e. half of the
total source energy goes into kinetic mass flow imparted to the
immediately surrounding liquid medium). This stored energy may only
contribute to the acoustic signal when the source motion reverses as in a
bubble cavity collapse.
In contrast with the impractical nature of solid state or monopropellant
liquid explosives for use as a source of high-power sonar system pulses,
gaseous explosions are potentially more practical by virtue of their
adjustable energy content, comparable energy conversion efficiency, pulse
repeatability and timing accuracy, and safety. Several forms of flexible
sleeve gas exploder devices have been used in marine seismic exploration
with generally good success. These devices are typically fueled by an
oxygen-propane mixture fed to the combustion chamber by one or more hoses
from a remote supply source and ignited by one or more remotely-controlled
spark plugs. Operation of these devices at near-surface water depths has
been a major advantage in providing simple design and reliable
performance. However, remote metering of the gas mixtures at depth can
lead to improper gas mixture variations which result in unreliable
ignition and significant differences in generated pulse energy. Use of
hydrocarbon fuels also produces exhaust gases which are troublesome in
sources that must operate at depth.
To circumvent this problem, several forms of oxygen-hydrogen flexible
sleeve exploders have been devised for use in the ocean and in boreholes
to depths of 4,000 feet and possibly deeper. The oxygen-hydrogen gas
mixture used in some of these devices has been derived by electrolysis of
in situ sea water whereas others used a self-contained supply of aqueous
electrolyte. By this electrolysis method, the generated oxygen and
hydrogen mixture is produced in approximately stoichiometric balance
independent of the pressure and depth conditions, resulting in more
accurate ignition, combustion energy uniformity, and acoustic pulse
repeatability. Combustion energy reactions up to about 200 kJoules per
pulse appear to be practical for typical sonar transducer depths and pulse
repetition rates in the range of about one pulse per minute, or less
frequent. Combustion reaction of a stoichiometric mixture of oxygen and
hydrogen forms steam as the sole combustion product which, upon
condensation, will return as water to the electrolyzer to be reused in a
closed-cycle repetitive gas generation and combustion process. By
selecting the aqueous electrolyte which produces the lowest practical
amount of chemically irreversible by-products in the closed-cycle
oxygen-hydrogen electrolysis process (i.e. the minimum excess
non-combustible chemical dissociation components and the minimum corrosion
contaminants from the electrolytic cell electrodes and electrolyte
chamber), the oxygen-hydrogen combustion process can be made accurately
repetitive and tolerant of long-term cyclic operation.
To date, none of these alternative source techniques have been found to be
practical either because of cumbersome and inefficient hardware or because
of their limited ability to generate the desired sound energy level at the
low frequencies of interest with directional specificity.
The present invention, based upon a gas combustion source concept, provides
the practical advantages of a high-energy density gas reaction, a simple
and safe closed-cycle source of the necessary fuel and oxidizing gases,
and associated means for achieving highly directional sound radiation
based either upon the flame front velocity in the combustible gas mixture
combined with the combustion chamber geometry and components or the use of
separate gas combustion elements in a spatial array combined with
prescribed ignition timing control.
SUMMARY OF THE INVENTION
The present apparatus and method utilizes an electrolysis process to
produce a stoichiometric mixture of oxygen and hydrogen gas which when
ignited burns with very high flame temperature while reacting to form
steam within a closed gas-generator combustion-chamber system. During each
combustion event, a substantial thermal pressure impulse is generated and
coupled to the surrounding seawater medium to produce a corresponding
acoustic impulse. Through this electrolytic and thermodynamic process,
latent chemical energy in the reactants as high as 100-200 kJoules may be
converted to sound wave energy in a chemically balanced and cyclic manner.
Thus, with only the input of electrical energy to the electrolysis
process, the oxygen-hydrogen combustion event occurs with negligible
byproducts to produce a high-energy sound pulse and the steam product of
combustion condenses and is returned to the electrolytic cell for reuse.
This process, employing reactants whose combustion products need not be
purged out of the combustion chamber after each cycle, is one of unusually
high energy density and, in analogy with other internal combustion
processes, has the potential for precise timing control. The electrical
input energy governs the combustion reaction energy and, correspondingly,
the associated acoustic energy. The size and physical design of the
combustion chamber governs the frequency spectrum of the radiated sound
wave pulse.
The intimate physical coupling and energy transfer of the combustion
reaction impulses into the surrounding water medium makes this transducer
technique exceptionally efficient; exceeded only by that of solid
explosive detonations for the desired low frequency sound signals of
interest. Accurate combustion pulse timing control allows several source
modules of this type to be operated with prescribed inter-element timing
in a multiple-element array to produce high energy acoustic pulses having
radiation directivity and a beam steering capability.
The present invention seeks to provide acoustic source transducers capable
of generating high-power underwater sound pulses having predominant
spectral content in the range of about 30-300 Hz and operating with good
energy conversion efficiency and accurate timing control. The
low-frequency pulse spectrum is necessary in order to minimize the
absorption losses along the longest practical sound propagation path while
also achieving effective acoustic backscattering. Source energy conversion
efficiency is important in reducing the primary power demand necessary to
drive the transducer and to minimize the size and weight of the source
system components. This factor combined with the ability to accurately
control the pulse initiation time, allows the source system to consist of
an array of high-power transducer elements which provide advantages in
spatial distribution of the source energy for better compatibility with
the linear energy density limit of the water medium and provide useful
beam forming directivity and beam steering.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the closed-cycle repetitive, acoustic pulse system in
simplified block form.
FIG. 2a illustrates a perspective view of the present invention.
FIG. 2b illustrates an end cross-section of the present invention.
FIG. 2c illustrates a partial side cross section of the present invention.
FIG. 3 illustrates an alternate embodiment of the present invention having
an array of separate combustion chambers.
FIGS. 4A and 4B illustrate a simplified view of the annular cylindrical
combustion chamber configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the present invention, the closed-cycle combustion-process
thermo-acoustic pulse source operates by first generating a stoichiometric
mixture of oxygen and hydrogen by electrolysis of water which is then
ignited to react by combustion. The combustion process generates a
thermally driven transient over-pressure relative to the local ocean
hydrostatic pressure to produce, via a flexible combustion chamber
interface, a radiated sound pressure impulse. The gaseous reactants
combine to produce water vapor which, by heat exchange with the
surrounding environment, condenses to water liquid which is returned to
the electrolytic cell to complete the cycle. This cyclic process takes
place in a self-contained subsurface transducer module designed to
accommodate the various states of the operating cycle at typical sonar
system immersion pressures. This modular system is energized by electrical
power transferred from the surface by an armored wireline cable which also
serves as the transducer suspension cable. Ignition of the combustion
pulse is provided by a high-voltage power supply and one or more spark
plugs contained in the transducer module. Ignition trigger pulses are
transmitted to the transducer module from a surface control unit. Source
system performance monitoring data are transmitted to the surface control
unit by telemetry circuits contained in the wireline cable.
FIG. 1 illustrates the closed-cycle repetitive acoustic pulse system in
simplified block diagram form. In operation, primary electrical power 11
from the surface control unit 12 and wireline cable 14 is conditioned in
the subsurface transducer module 16 to operate the electrolytic cell 18
and to supply a high-voltage ignition spark 20 when triggered from the
surface control unit 12. The electrolytic cell or electrolyzer 18
generates an accurately stoichiometric mixture of oxygen and hydrogen gas
22 which flows into the flexible-wall combustion chamber 24 building up a
chemical combustion charge whose energy content is dependent upon the
effective current flow through the electrolytic cell. The gas mixture in
the combustion chamber will become pressurized as the electrolysis process
proceeds, acting against the hydrostatic pressure external to the chamber.
[Normally, prior to operational use, the combustion chamber will be
evacuated and the electrolyte degassed to remove any nonreacting gases
which would otherwise moderate the combustion temperature or produce
potentially contaminating by-products.]
When a firing trigger pulse 26 is transmitted to the subsurface module 16,
the gas mixture in the combustion chamber 24 will be ignited and will burn
rapidly to produce high-temperature steam at a substantial pressure rise
proportional to the pre-combustion chamber pressure at the time of
ignition. The incompressible seawater medium surrounding the combustion
chamber 24 is directly subjected to the combustion pressure pulse and will
transmit an acoustic pressure impulse 28 whose far field peak amplitude
will depend upon the motional velocity of the combustion chamber wall.
Internal steam pressure, mechanical compliance of the chamber wall, heat
storage and transfer from within the chamber, and kinetic energy in the
surrounding medium interact to absorb the non-acoustic residual energy of
the combustion process representing the energy deficit which would
otherwise allow the chemical-to-acoustic energy conversion efficiency to
be 100 percent. The much slower collapse rate of the chamber, related
primarily to the condensation rate of the steam, will produce a weaker and
time delayed secondary acoustic pressure impulse, similar to the steam
bubble collapse pulse of an underwater explosion, which will radiate into
the far field as an indirect contribution to the acoustic efficiency of
the source. Water 30 from the condensed steam is returned to the
electrolytic cell where it is reused in the next pulse cycle.
The electrolysis process used to dissociate the aqueous electrolyte into
oxygen and hydrogen is relatively inefficient because of electrical
heating inherent in conducting current through the bulk liquid (gas
generation results only from the half-cell reactions at the electrodes).
Power losses in the electrolyte and the needed gas production rate govern
the size and heat transfer capacity of the electrolyzer. For a given
geometric cell design, the gas production efficiency may be optimized by
adjusting the conductivity of the electrolyte solution. Dilute aqueous
solutions of strong acids (e.g. sulfuric acid) or bases (e.g. sodium
hydroxide) are most commonly used in oxygen-hydrogen electrolytic
generators. The chemical nature of these electrolytes will govern the
choice of the materials used to construct the electrolytic cell. The
preferred electrode materials are the noble metals although
corrosion-resistant stainless steel or certain conducting polymers well
known in the art may serve as suitable alternative electrodes when used
with certain electrolytes.
An electrolytic cell or electrolyzer using a sodium hydroxide aqueous
electrolyte will produce a stoichiometric mixture of oxygen and hydrogen
at an efficiency of about 25 percent when comparing the produced gas
constituent heating value energy with the electrical energy input. A
simple one-stage cell will produce 8.306.times.10.sup.-5 g/sec of oxygen
and 1.038.times.10.sup.-5 g/sec of hydrogen per ampere of current flow.
The voltage drop across an ideal (100-percent efficient) electrolytic cell
is 1.277 volt neglecting any power losses in the bulk liquid electrolyte.
For electrolyte concentrations which yield only the desired stoichiometric
gas mixture (no other adverse electrode reactions) a typical cell voltage
will be approximately 2.0 volts, taking into account the bulk liquid
voltage drop. Considering the remote operating requirement of the
transducer, with the wireline cable as a significant part of the
electrolytic power delivery circuit, a series cascade of such cells offers
a practical design approach. Thus, given a wireline cable having a
specific voltage rating and conductor resistance, there will be an optimum
number of electrolytic cells for maximally efficient gas production.
Further, although not necessarily a constraint in low repetition rate
acoustic pulse source systems, the maximum gas production energy rate will
generally be limited by the wireline cable. As a preliminary design
configuration, the electrolytic cell may consist of 50-100 cascaded stages
operating at a series current of about 8-10 amperes supplied by a surface
sending end voltage of 2-300 volts on the wireline cable. In such a case,
a 100-stage cell will generate about 10 liters of hydrogen at standard
temperature and pressure per minute; a useful production rate that may be
increased, if necessary, by a factor of 2-4 to meet higher energy or rapid
pulse repetition rate operation. The associated latent chemical energy
content of a stoichiometric mixture of 10 liters of hydrogen and 5 liters
of oxygen is 67,760 Joules and, in complete closed cycle operation, is
determined from the lower heating value of hydrogen. An increase of about
three times this energy input to the combustion process (i.e. to about 200
kJ) is anticipated to shift the system operational limitations from the
wireline power handling capacity to the heat transfer design of the
electrolytic cell and to the strength of materials used in the flexible
sleeve combustion chamber. This limit is also estimated to be in excess of
the linear acoustic energy density characteristics of the water medium
except at very deep depths.
The combustion process is one of very rapid burning of the gas reactants in
which typical flame front velocities are in the range of 1,000-2,000
m/sec. Thus, for well mixed gases, the combustion time duration will be in
the range of about 1 msec and will produce peak temperatures in the range
of about 2,500.degree.-3,000.degree. K. When the combustion process occurs
at constant volume, then an estimate of the peak combustion overpressure
is
P.sub.pk .apprxeq.(T.sub.max /T.sub.amb)P.sub.amb ;
a value corresponding to about eight to ten times the ambient immersion
hydrostatic pressure of the transducer. By coupling this pressure impulse
to the surrounding seawater through the flexible interface of a
high-temperature-rated elastomer sleeve, the chemical reaction energy of
the oxygen-hydrogen mixture is efficiently transferred to acoustic and
kinetic energy in the water medium. The combustion process induces high
tensile stresses in the elastomer and exposes its inner surface to
high-temperature steam. Therefore, a tough high-temperature elastomer such
as Kalrez (Dupont) or similar material is required and an
expansion-limiting outer cage may be used to restrict the physical
expansion of the sleeve. Ignition of the gas mixture may be hindered by
any residual water condensate in the combustion chamber. Therefore,
several independently fired spark plugs should be located within the
combustion chamber and heated to prevent fouling.
The physical size and combustion energy of the transducer are factors that
establish the practical physical scale and material stress limits.
Combustion chamber volumes ranging from about 15 in.sup.3 to 60-80
in.sup.3 cover the practical range for the low-frequency high-power
acoustic impulses of interest in the present invention, i.e., 30-300 Hz.
FIGS. 2a, 2b, 2c and 3 illustrate towed arrays of the present invention 10
described above. In FIG. 2(a), the rectangular strut 40 along the central
length of these arrays is the rigid strength member of the assembly
whereas the upper 41 and lower 44 cylindrical sections form the flexible
combustion chambers and the rigid electrolysis cells, respectively.
Stabilizing fins 46 near the forward end maintain the array vertically
oriented with the combustion sleeve 48 at the top and the electrolysis
cells 50 at the bottom.
FIG. 2(b) illustrates an end cross-section of the device, showing the
electrolytic cell 50 containing an aqueous electrolyte 52 at the bottom
and the flexible sleeve 48 and an internal core body 54 at the top.
The internal core body may be a rigid member extending the length of the
chamber. The core size may vary to determine the volume of oxygen and
hydrogen which may be received in the chamber. The rectangular strut 40
provides passageways 46 for oxygen and hydrogen gas to enter or
communicate with the combustion chamber 42 and to tend to inflate the
sleeve 48 in the concave rib zones 58 around the internal core 54.
Numerous gas passage holes 60 perforate the core to permit free movement
of the gas mixture before combustion and to permit drainage of the
condensed water after combustion.
FIG. 2(c) shows a side cross-section illustrating two of the adjacent
electrolysis cells 50 and 51 and their parallel electrical connections.
The cascade of multi-electrodes in each electrolysis cell consists of
50-100 electrode plates designed to operate at 100-200 volts applied at
each end; the ends being electrically connected at common voltage
polarities to force proper current flow through each cell. The evolved
oxygen and hydrogen are mingled directly upon liberation and rise upward
through narrow passageways 46 in the strength member strut 40 to enter the
combustion chamber 42. In the continuous combustion chamber shown, the
combustion process is initiated at the forward end 62 of the chamber and
the resulting combustion pulse travels at the flame-front velocity to the
aft end 64 of the chamber. The sound wave impulse generated in the
surrounding seawater is directed aft of the towed array. The shape and
perforated characteristics of the internal core 54 within the flexible
sleeve 48 is designed to influence and adjust the oxygen-hydrogen
flame-front velocity to be approximately equal to the velocity of sound in
sea water at the typical depth intended for the source transducer
operation. Operating power and ignition control signals are supplied from
the surface vessel via the towing cable 66.
The directional underwater acoustic pulse source 10 has the following:
(1) High impulsive sound energy created by the combustion reaction of
stoichiometrically mixed oxygen and hydrogen.
(2) Closed-cycle combustion operation involving cycle steps wherein water
is first decomposed by electrolysis to produce oxygen and hydrogen in
stoichiometric proportions, the oxygen and hydrogen mixture is next
ignited to cause a rapid impulsive chemical reaction and associated
thermal expansion process in which the only combustion by-product is
steam, and finally the steam cools and condenses to water which is
returned to the electrolysis process for reuse.
(3) The combustion chamber in which the oxygen and hydrogen gases react is
a flexible sleeve through which the impulsive pressure associated with the
heat of combustion imparts a pressure into the surrounding medium (sea
water) to produce an impulsive shock wave or sound wave having an acoustic
energy level which is a substantial fraction of the chemical energy of the
reactant gases.
(4) The flexible-sleeve combustion chamber consists, in a first form, of a
tubular elastomer channel in which combustion of the contained reactant
gases is initiated at a first end, the resulting combustion process
travels along the sleeve toward the second end at a flame-front velocity
which is dependent upon the combustion gas constituents, their ambient
conditions, and the sleeve geometry, whereafter the combustion cycle ends
when the flame front reaches the second end of the flexible sleeve.
Thermal expansion of the reacting gases forms a traveling pressure front
in the flexible sleeve, pressurizing and expanding the sleeve outwardly
against the surrounding seawater medium and, thereby, progressively
generating generally uni-directional acoustic sound waves in the water
along the length of the sleeve. The flexible sleeve geometry causes the
combustion flame-front velocity to be approximately the same as the speed
of sound in the surrounding sea water medium; part of the combustion
pressure pulse energy efficiently transformed into a radiated sound wave.
The combustion pressure pulse, traveling at the speed of sound in sea
water along the length of the flexible sleeve, acts in a constructive way
to inherently reinforce the water-borne sound wave traveling in the
direction of the combustion pulse. This process discriminates against
soundwaves radiated in the direction opposite to that of the traveling
combustion pulse, resulting in a one-dimensional line radiator having a
preferential "end-fire" sound radiation pattern along the longitudinal
sleeve axis in the direction of the traveling combustion pulse.
(5) The flexible-sleeve combustion transducer may consist, in an alternate
embodiment as shown in FIG. 3, of an array of separate combustion
compartments or modules, fed either from a common electrolytic gas
generator or from individual electrolytic gas generators, and having
independent ignition circuits and ignition timing control. By placing
these modular elements in a prescribed spatial array relationship, and
controlling their pulse ignition times in prescribed relationships, the
array can produce desirable sound radiation patterns which may be adjusted
in beamwidth and direction. For example, when such a modular array
containing a number of closely spaced elements is arranged in a straight
line and the modules triggered at delayed ignition times beginning at a
first end and ending at an opposite end, then a discrete-element array
similar to the continuous-sleeve concept described is obtained. Efficient
end-fire sound radiation is obtained from this discrete-element array when
the ignition delay times between adjacent elements are the same as the
sound pulse travel time in the surrounding sea water as governed by the
spacing distances between the adjacent elements and the speed of sound in
the sea water.
FIGS. 4a and 4b illustrate a simplified physical layout of the annular
cylindrical combustion chamber configuration. The rigid center body 54 of
the combustion chamber 42 is employed to increase the surface area of the
active surface of the source and to provide control of the volume
displacement of the source independent of the combustion chamber volume.
The design parameters of the pulse source of FIGS. 4a and 4b are as
follows:
______________________________________
Preliminary Design of a Oxygen-Hydrogen
Combustion Pulse Source
______________________________________
Number of electrolysis Cells:
75
Length of Combustion Chamber
1.0 m
Annular Volume of Combustion
3.14 l = 3.14 .times. 10.sup.-3 m.sup.3
Chamber: D.sub.o = 0.254 m
D.sub.i = 0.246 m.
Applied Voltage (75 cells)
97.5 V (rms) (neglecting
electrolyte voltage drop)
Current in 75-Cell Cascade:
10 A (rms)
Operating Power: 975 W.
Charging time to store 236 kJ
240 sec (4 min)
latent energy:
Peak Combustion Impulse
9.786 .times. 10.sup.6 Pa (1,419 psig)
Pressure: (At depth of 100 m in seawater
P.sub.100 = 1.0074 .times. 10.sup.6 Pa)
______________________________________
The combustion chemical-to-electrical energy conversion efficiency, for the
conditions carried through this analysis, is
##EQU1##
It should be understood that this result neglects the power dissipated in
the electrolyte between the plates and the fact that current can flow
around the cascade of electrodes without contributing to the electrolysis
process. An estimate of the practical energy conversion efficiency is
derived on the basis that the bypass current is equal to the electrolysis
current and the cell voltage drop is three times that required for
electrolysis (i.e. 3.times.1.3=3.9 V where 1.3 V is the half-cell voltage
drop at each electrode surface). Thus, the resistances in the electrolysis
current path (R.sub.e) and in the bypass current path (R.sub.b) are
##EQU2##
Therefore, for a gas generating current of I=10 A, the nonproductive power
loss in the electrolyte (per cell) is
##EQU3##
Therefore, the approximate electro-chemical energy conversion efficiency,
for a gas producing power of P.sub.g =1.3.times.10=13 w, is
##EQU4##
based upon a single-cell model with bypass current.
As a projection of the typical limit of improvement in this efficiency, if
no bypass current existed the electrolyte losses would be reduced from 65
watts to 26 watts and the resulting efficiency would be
##EQU5##
For a 75-cell cascade electrolyzer, the excitation voltage required for
operation in the case involving electrolyte losses is
##EQU6##
and, for a total electrolyzer current of I.sub.T =I+I.sub.b =20 A (rms),
the excitation power to the 75-cell electrolyzer operating at 100 percent
duty cycle (one combustion pulse every four minutes) is
##EQU7##
at 16.7 percent electro-chemical conversion efficiency.
While the invention has been described in connection with a preferred
embodiment, it is not intended to limit the invention to the particular
form set forth, but, on the contrary, it is intended to cover
alternatives, modifications, and equivalents, as may be included within
the spirit and scope of the invention as defined by the appended claims.
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